Plant Movements

Abstract

Terrestrial plants are sessile and are incapable of changing their location. Yet, plants can sense their environment and can respond to sensory information through visible movements to optimize their survival, growth, and reproduction. The earliest findings published in this field were from Charles Darwin in 1880 in his book entitled The Power of Movement in Plants that explored the phenomenon of phototropism. Plant movements can be defined as the changes in the spatial orientation or conformation of an organ or its parts. Plant movements include movements toward light, opening and closing of flowers, growth of developing roots in search of water and nutrients, etc. In fact, inflorescence, fruits, and shoots are all capable of moving by sensing changes in environment, thereby adjusting their position, function, and behavior accordingly. Plant movements are extremely slow and often undetectable. Classical examples of visible plant movements include the response of sensitive plants like “touch-me-not” (Mimosa pudica) and the carnivorous Venus flytrap (Dionaea muscipula). In addition to whole organ, the movement of single cells is also possible which includes, for example, the movement of guard cells, which regulates the stomatal pore size, as well as growth of the pollen tube through the style. Such movements are caused by motor cells, driven by changes in pressure from within the cells exerted against the cell walls. Pressure causes changes in the dimensions of individual cells or tissues which results in distinctive movements. Plant movements are classified as:

Multiple-Choice Questions

• 1. Pea tendril coiling around a support is an example of:

  • (a) Thermotaxis

  • (b) Thigmonasty

  • (c) Thigmotaxis

  • (d) Thigmotropic

• 2. Curving of plant toward light is called:

  • (a) Thigmotropism

  • (b) Gravitropism

  • (c) Phototropism

  • (d) Thigmonasty

• 3. Sleep movements are mediated by turgor changes in specialized motor cells located in:

  • (a) Pulvinus

  • (b) Stem

  • (c) Leaf blade

  • (d) Root

• 4. Roots perceive gravity by a mechanism that involves sedimentation of:

  • (a) Chloroplasts

  • (b) Statoliths

  • (c) Ribosomes

  • (d) Mitochondria

• 5. Which of the following is not true for nastic movements?

  • (a) Depend on the direction of the stimulus

  • (b) Are independent of the direction of the stimulus

  • (c) Genetically predetermined

  • (d) Driven by growth or turgor changes

• 6. Circadian rhythm is a biological rhythm with a cycle of:

  • (a) 12 hours

  • (b) 24 hours

  • (c) 36 hours

  • (d) 48 hours.

• 7. Curvature of the stem due to phototropic movement is due to uneven distribution of:

  • (a) Cytokinin

  • (b) Auxin

  • (c) Phytochrome

  • (d) Gibberellin

• 8. Folding of leaflets of Mimosa pudica is associated with the efflux of:

  • (a) Calcium ions

  • (b) Magnesium ions

  • (c) Potassium ions

  • (d) Chloride ions

• 9. ___________ cells function as multicellular motors in the leaves of grasses cause extensive changes in leaf conformation.

  • (a) Guard cells

  • (b) Bulliform cells

  • (c) Subsidiary cells

  • (d) Lenticels

• 10. Carnivorous plants entrap their prey in traps driven by:

  • (a) Turgor-mediated changes

  • (b) Growth

  • (c) Contraction

  • (d) Locomotion

Answers

1.b	2.c	3.a	4.b	5.a	6.b	7.b
8.c	9.b	10.a